1. Field of the Invention
This invention relates to an improved process for providing magnetic bubble domain systems, and in particular to a process for providing high density bubble domain systems using only a single critical masking step.
2. Description of the Prior Art
Various systems using magnetic bubble domains are known in the art. For example, a self-contained magnetic bubble domain memory chip using a decoder is shown in U.S. Pat. No. 3,701,125. Additionally, a major/minor loop memory configuration is shown in U.S. Pat. No. 3,618,054. As will be noted, provision of complete memory systems requires that some or all of the functions of read, write, propagation, transfer, and annihilation be provided. That is, bubble domains are generated for representation of information, and these bubble domains generally have to be propagated in the system. After propagation, they are read and then annihilated or returned to their storage locations. Additionally, these systems often require transfer functions where bubble domains are transferred from one propagation path to another, usually by the use of current carrying loops that produce magnetic field gradients for the transfer.
Many components are known in the art for generating magnetic bubble domains and for detecting these bubble domains. For example, a magnetoresistive sensing technique is shown in U.S. Pat. No. 3,691,540. For the function of storage, bubble domains are generally propagated using any of many well-known structures. In particular, high density structures are known using ion implanted regions in the bubble domain material for restraining and moving magnetic bubble domains, in combination with a reorienting magnetic field in the plane of the bubble domain material. Such ion implanted structures are described by R. Wolfe et al in the AIP Conference Proceedings, No. 10, Part 1, p. 339 (1973), which Proceedings contain the text of the papers delivered at the 18th Annual Conference on Magnetism and Magnetic Materials, held in Denver, Colo., in 1972.
The processes used for making magnetic bubble domain chips has developed through the years so that single level masking techniques are now used. In such techniques, the magnetic sensors are deposited using the same mask as is used for depositing the magnetic propagation elements. Additionally, since the propagation elements are not in contact with one another, conductors can be placed directly over the propagation elements without shorting any electrical currents. This means that the bubble domain chip can be fabricated using only a single critical masking step.
However, the prior art does not address the problem of making high density magnetic bubble domain chips where the propagation elements are contiguous with one another. In such systems, it is difficult to place conductors directly on the propagation elements, since electrical shorting may occur. Additionally, several critical masking steps are usually required in order to define the sensors, propagation elements, and conductors used for bubble domain transfer and sensor current. Because this is a critical problem when bubble domain technology is to be used to provide economical, high density structures, the present invention seeks to provide a process for providing such a high density magnetic bubble domain chip using a minimum number of masking steps, only one of which is critical.
Accordingly, it is a primary object of this invention to provide a process for fabricating high density magnetic bubble domain chips in which only one critical masking step is required.
It is another object of this invention to provide a process for fabricating a magnetic bubble domain chip having contiguous propagation elements requiring a minimum number of masking steps.
It is still another object of the present invention to provide a high density magnetic bubble domain chip having components for generation, reading, propagation, transfer, and annihilation, all of which components require a resolution less than 5d, where d is the bubble domain diameter.
It is a further object of this invention to provide an improved process for fabricating a high density magnetic bubble domain chip using ion implanted propagation elements, magnetic sensors and annihilators, and current carrying lines for generation, sensing, and transfer.